Creating Content Types Based on Other Content Types
You can create site content types based on other site content types. To do this, the site on which you are creating your new content type must be in scope for the site content type from which you are deriving the new content type. For more information on content type scope, see Content Type Scope.
In this way you can create a general site content type, which contains attributes common to several types of content, and then derive more specific site content types from it. This is exactly what Windows SharePoint Services does in its own built-in content type hierarchy. All content types ultimately derive from the System content type. For more information on hierarchy of content types included in Windows SharePoint Services, see Base Content Type Hierarchy.
The following figure shows this. In this example, the site collection root site contains three site content types. Two of those, Memo and Spec, are actually based on the third, Document. Because Document contains the column Author, that column is common to all three. A child site further extends the Spec site content type to create a new template, ProductXSpec. This new template contains all the columns from Spec, as well as an additional column, SKU. When you apply the ProductXSpec site content type to a list, and Windows SharePoint Services copies it locally as a list content type, all four columns are added to that list, if they have not been added already.
You can edit any attribute of a site content type you derive from another site content type in the following ways:
Add, alter, or remove columns.
Specify different New, Edit, or Display forms.
Specify a different document template; and so on.
For more information on the predefined content type hierarchy included in Windows SharePoint Services, see Base Content Type Hierarchy.